Chelsea fans turned on manager Liam Rosenior during a 3-0 defeat to Brighton.
Max Verstappen has led the disapproval, with revisions now made to regulations ahead of the Miami Grand Prix.
The breakaway competition launched in 2021 but speculation has mounted that the Saudi Public Investment Fund (PIF) is set to end its backing.
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The Real Madrid midfielder, who began his career with Birmingham, is thought to have invested around £800,000 in the Edgbaston-based team.